Bio-microrheology is the quantitative study of mechanical properties of live cells. Variations in mechanical properties are intrinsic indicators of ongoing cellular processes such as increase in elasticity of certain cancer cells, change of membrane stiffness in malaria-infected red blood cells, and changes in cellular adhesion, for example. The measurement of rheological properties of cell membranes is advantageous since it may also indirectly provide information on the internal structures of cell. A number of different techniques exist to assess membrane rheological properties of live cells. These include atomic force microscopy (AFM), optical and magnetic tweezers, pipette aspiration, electric field deformation, and full-field transmission phase microscopy. Many of these methods use large deformations that can lead to a non-linear response. For point-measurement techniques such as AFM, the time scales to probe large surface areas of a cell membrane are in minutes, preventing the study of high-speed cell membrane dynamics over a wider surface area. Transmission phase microscopy has been successfully utilized to measure membrane rheological properties of red blood cells that have 2-D bilayer cytoskeleton. However, most types of cells have complicated 3-D internal cellular structures, rendering most of the above techniques unsuitable as they probe a combination of membrane as well as bulk properties of cells that are difficult to decouple.
Thus further improvements are needed in the field of phase microscopy for measuring complex biological systems as well as other applications in scientific and industrial metrology.